# How do you solve the following system: x + 8y = 15 , x + 4y = -2 ?

Dec 18, 2015

$x = - 19$
$y = \frac{17}{4}$

#### Explanation:

You can already say with the 2nd equation that $x = - 2 - 4 y$.

You replace x by its new expression in the 1st line :

$x + 8 y = 15 \iff - 2 - 4 y + 8 y = 15 \iff 4 y = 17 \iff y = \frac{17}{4}$

You now replace y by its value in the second equation !

$x = - 2 - 4 y \iff x = - 2 - 17 \iff x = - 19$